Work in clinical analysis requires the investigator to evaluate a given sample to determine whether a particular analyte of interest is present, and if so, in what amount. Such information is extremely valuable in diagnosis and treatment of patient. The analyses referred to supra are being carried out, more and more frequently, using automated methods. These methods are diverse, but generally involve the preparation of a sample which is then introduced to an automatic analyzer. The analyzer is set up to carry out various reactions designed to measure the analyte or analytes of interest, and to determine a particular value or "signal" associated with these reactions. Sophisticated automated systems convert these reading into a value indicative of the analyte's presence or concentration, thereby providing the investigator with a precise determination of the particular analyte of interest.
The analytical systems outlined supra, as well as any analytical system used for clinical purposes requires that a control be used. Such controls permit the investigator to check the accuracy of the system being used. In clinical diagnosis where some analytes are present in only vanishingly small amounts, and where minute changes in levels mean the difference between normal and pathological conditions, a satisfactory control reagent becomes an integral, and critical part of the analytical system.
Control reagents should be as similar to the sample type for which they serve as a control as possible. Biological fluids such as blood and serum, e.g., are extremely complex compositions, however, and there are many examples of formulations designed to be as close as possible to biological fluids and to serve as controls therefor. A cursory sampling of the patent literature in this area includes, e.g., U.S. Pat. Nos. 4,678,754 (Hoskins); 4,643,976 (Hoskins); 4,529,704 (Tremner et al.); 4,438,702 (Engler et al.); 4,405,718 (Rapkin et al.); 4,372,874 (Modrovich); 4,301,028 (Barth et al.); 4,276,376 (Hundt et al.); 4,260,579 (Barton et al.); 4,230,601 (Hell); 4,199,471 (Louderback et al.); 4,193,7666 (Dounora et al.); 4,127,502 (Li Mutti et al.); 4,126,575 (Louderback); 4,123,384 (Hundt et al.); 4,121,905 (Maurukas): 4,054,488 (Marbach); 4,078,892 (Steinbrink, Jr); 3,973,913 (Louderback); 3,920,580 (Mast); 3,920,400 (Scheibe et al.); 3,859,047 (Klein); 3,466,249 (Anderson); 3,852,415 (Vandervoorde); 3,274,062 (Lou); 3,260,648 (Fox). The approaches taken in these patents vary. Many of them teach control reagents useful for determining one, or a family of a few related analytes. Others are more general, and relate to improvements in the field in general. It is the latter group to which the present invention belongs.
As was noted supra, attempts are made within the art to formulate control reagents that are as close to the type of material for which they are controls as possible. As a result, control reagent are frequently based upon blood, plasma, or serum, be these human or mammalian (e.g., bovine).
Control reagents of the type discussed supra do have certain drawbacks, which are inherent in any natural product based material. For this, and other reasons, the art has also contemplated and used control reagents which are serum free. Generally, these water based control reagents have to be substantially modified so as to make them as close to a biological sample as possible. An example of such a modification is the inclusion of a polymeric viscosity agent, to make the reagents' rheological properties as close to biological samples as possible.
A major problem with all control reagents is the tendency of the analyte of interest to undergo chemical reactions in situ, thereby leading to false results when the control is in fact used. An example of such a chemical reaction is simple oxidation. Oxidized analyte, or analyte which otherwise reacts prior to use of the control system, leads to shifts in signal formation and away from true control values. Generally, these controls produce a greater signal than a corresponding amount of analyte in a sample being analyzed.
It has now been found, surprisingly, that control reagents can be prepared where the problem alluded to supra is avoided, without any disruption in the chemistry of the stabilized system. The invention, elaborated upon more fully infra, involves the incorporation of at least one antioxidant or one hydroxylamine into a liquid based control reagent which also contains a known amount of at least one analyte. The resulting material, referred to hereafter as a stabilized control reagent, is useful in the same way any control reagent is useful.